Waste material processing apparatus

ABSTRACT

A material processing apparatus includes a casing having a top and bottom and a plurality of sides defining a pyrolysis chamber for receiving and pyrolyzing feed materials therein into fluid materials and a mass of refractory material disposed upon the bottom of the casing and spaced below the top thereof and extending between its sides. The refractory mass includes an upper surface defining a bottom of the pyrolysis chamber and having an end spaced from a first one of the casing sides to define an ash residue collection cavity therebetween. The apparatus also includes a system of tunnels defined within the refractory mass being spaced below the upper surface thereof. The system of tunnels includes an inlet defined in the refractory mass at the end thereof and below the upper surface thereof and in communication with the cavity for receiving a flow of materials from the pyrolysis chamber into the system of tunnels and an outlet defined in a second one of the sides of the casing for discharging the flow of materials from the system of tunnels. The apparatus also includes elongated heater units mounted to sides of the casing and extending into and axially along selected ones of the tunnels in the system thereof.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the priority of copending Provisional PatentApplication Ser. No. 60/084,743, filed May 8, 1998, entitled WASTEMATERIAL PROCESSING APPARATUS AND METHOD.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to material processing and, moreparticularly, is concerned with an apparatus for controlled processingof materials and a method of controlling hydrocarbon release rate bymaintaining target oxygen concentration in discharge gases so as tothereby convert successive batches of materials of widely varying energycontent into substantially harmless gases and carbon-free residue ash,such as is necessary for the disposal of medical and other diverse wastematerial, particularly on-site where the waste material is produced.

2. Prior Art

The problem of disposal of waste matter involves a material processingchallenge that is becoming increasingly acute. The primary materialprocessing methods of waste disposal have been burning in incineratorsand burial in landfills. These two material processing methods havesevere disadvantages. Burning of waste liberates particulate matter andfumes which contribute to pollution of the air. Burial of wastescontributes to the contamination of ground water. A third materialprocessing method is recycling of waste. Although increasing amounts ofwaste are being recycled, which alleviates the problems of the twoprimary material processing methods, presently available recyclingmethods do not provide a complete solution to the waste disposalproblem.

The problem of disposal of biomedical waste materials is even moreacute. The term "biomedical waste materials" is used herein in a genericsense to encompass all waste generated by medical hospitals,laboratories and clinics which may contain hazardous, toxic orinfectious matter whose disposal is governed by more stringentregulations than those covering other waste. It was reported in The WallStreet Journal in 1989 that about 13,000 tons a day of biomedical waste,as much as 20% of it infectious, is generated by around 6,800 U.S.hospitals.

Hospitals and other generators of biomedical waste materials haveemployed three main material processing methods of waste handling anddisposal: (1) on-site incineration with only the residue transferred tolandfills; (2) on-site steam autoclaving and followed by later transferof the waste to landfills; and (3) transfer of the waste by licensedhazardous waste haulers to off-site incinerators and landfills. Of thesethree main material processing methods, theoretically at least, on-sitedisposal is the preferred one.

However, many hospital incinerators, being predominantly located inurban areas, emit pollutants at a relatively high rate which adverselyaffect large populations of people. In the emissions of hospitalincinerators, the Environmental Protection Agency (EPA) has identifiedharmful substances, including metals such as arsenic, cadmium and lead;dioxins and furans; organic compounds like ethylene, acid gases andcarbon monoxide; and soot, viruses, and pathogens. Emissions of theseincinerators may pose a public health threat as large as that fromlandfills.

Conventional incinerators most commonly are designed to operate above acertain temperature, such as 1200°-1400° F., to comply with requirementsof the permit laws of many states. The reason for this requirement isthat conventional thinking has been that operation of incinerators atsuch elevated temperatures will substantially eliminate the release ofmost harmful substances. This may have been true where the materialsbeing consumed by the incinerator were assumed to be fairly uniform interms of energy content and thus burned more or less evenly. However,this is the exception and not the normal situation today, particularlyin the case of biomedical waste materials which can range from wet papertowels and steel surgery tools to plastic syringes and containers ofsaline solution. The thermal processing of these materials bytemperature control alone will ordinarily result in the inability tocontrol the hydrocarbon release rate and the repeated emission ofun-burned hydrocarbons, typically visible as periodic puffs of blacksmoke, which is unacceptable under most current environmentalregulations.

Nonetheless, on-site disposal of biomedical waste materials stillremains the most promising solution. One recent on-site waste disposalunit which addresses this problem is disclosed in U.S. Pat. No.4,934,283 to Kydd. This unit employs a lower pyrolyzing chamber and anupper oxidizing chamber separated by a movable plate. The waste materialis deposited in the lower chamber where it is pyrolyzed in the absenceof air and gives off a combustible vapor that, in turn, is oxidized inthe upper chamber. While this unit represents a step in the rightdirection, it does not appear to approach an optimum solution to theproblem of biomedical waste material disposal.

One problem with the approach of the aforementioned patent is that itproposes the use of an on-site waste disposal unit which is dedicated tothe disposal of biomedical waste material. This approach requires thatmore than one incineration system be installed and maintained athospitals, namely, one for biomedical waste and another for all otherhospital waste. Resistance has been encountered to the adoption of thisapproach by hospitals due to added cost of installation, operation andmaintenance. An urgent need has developed for an all-purpose materialprocessing apparatus which can handle disposal of all types of hospitalwaste materials, both biomedical waste and general waste, such as metalneedles and glass and plastic bottles.

Reference is also made to the following issued U.S. Patents dealing withsubject matter related to the present invention, the disclosures ofwhich are hereby incorporated in their entireties:

1. "Apparatus And Method For Controlled Processing Of Materials" byRoger D. Eshleman and Paul S. Stevers, assigned U.S. Ser. No. 07/987,928and filed Dec. 9, 1992 and issued U.S. Pat. No. 5,353,719.

2. "Multiple Unit Material Processing Apparatus" by Roger D. Eshleman,assigned U.S. Ser. No. 07/987,929 and filed Dec. 9, 1992, and issuedU.S. Pat. No. 5,289,787.

3. "Heat Generator Assembly In A Material Processing Apparatus" by RogerD. Eshleman, assigned U.S. Ser. No. 07/987,936 and filed Dec. 9, 1992,and issued U.S. Pat. No. 5,338,918.

4. "Casing And Heater Configuration In A Material Processing Apparatus"by Roger D. Eshleman, assigned U.S. Ser. No. 07/987,946 and filed Dec.9, 1992, and issued U.S. Pat. No. 5,420,394.

5. "Apparatus And Method For Transferring Batched Materials" by Roger D.Eshleman, assigned U.S. Ser. No. 08/026,719 and filed Mar. 5, 1993,issued U.S. Pat. No. 5,338,144.

6. "Sloped-Bottom Pyrolysis Chamber And Solid Residue Collection SystemIn A Material Processing Apparatus" by Roger D. Eshleman, assigned U.S.Ser. No. 08/299,034 and filed Sep. 17, 1993, issued U.S. Pat. No.5,417,170.

7. "Material Transport Pusher Mechanism In A Material ProcessingApparatus" by Roger D. Eshleman, assigned U.S. Ser. No. 08/123,747 andfiled Sep. 17, 1993, issued U.S. Pat. No. 5,361,709.

8. "Improved Casing And Heater Configuration In A Material ProcessingApparatus" by Roger D. Eshleman, assigned U.S. Ser. No. 08/123,454 andfiled Sep. 17, 1993, issued U.S. Pat. No. 5,428,205.

9. "Method of controlling hydrocarbon release rate by maintaining targetoxygen concentration in discharge gases" by Paul H. Stevers, assignedU.S. Ser. No. 08/283,118 and filed Jul. 29, 1994, issued U.S. Pat. No.5,501,159.

SUMMARY OF THE INVENTION

The present invention provides a diverse material processing apparatusdesigned to satisfy the aforementioned needs. While the apparatus of thepresent invention can be used in different applications, it is primarilyuseful as an apparatus for waste disposal and particularly as anapparatus for disposing of biomedical and general hospital wastematerial on-site where the waste material is produced. A greater than95% reduction in mass and volume is achieved as is the completedestruction of all viruses and bacteria. The residue is a sterile, inertinorganic powder, which is non-hazardous, non-leachable and capable ofdisposal as ordinary trash.

The preferred embodiment of the present invention includes variousunique features for facilitating the processing of material andparticularly the disposing of diverse waste material. Although some ofthese features may form a part of the inventions claimed in the patentscross-referenced above, these features are illustrated and describedherein for facilitating a complete and thorough understanding of thosefeatures comprising the present invention.

Accordingly, the present invention is directed to a material processingapparatus which generally comprises: (a) a casing having a top, a bottomand a plurality of sides defining a pyrolysis chamber for receiving andpyrolyzing feed materials into fluid materials and including an upperportion for temporarily receiving the fluid materials and wherein atleast one of the plurality of sides includes a down-draft duct having(i) an entrance positioned in flow communication with the upper portionof the pyrolysis chamber, and (ii) an exit spaced from the entrance; (b)a mass of refractory material contained in the casing and spaced belowthe top and extending between the sides, the refractory mass includingan upper surface defining a bottom of the pyrolysis chamber and havingan end being spaced from a first one of the sides of the casing so as todefine an ash residue collection cavity; and (c) a system of tunnelsdefined within the refractory mass and spaced below the upper surfacethereof, the system of tunnels including at least one inlet defined inthe refractory mass adjacent to an end thereof and below the uppersurface and in flow communication with the exit of the down-draft ductso as to receive a flow of the fluid material from the pyrolysis chamberinto the system of tunnels and an outlet defined in a bottom of thecasing for discharging the flow of materials from the system of tunnels.

In one preferred embodiment, the system of tunnels includes (a) a pairof spaced upper tunnels, each one of the pair of upper tunnels beingdisposed in flow communication with an inlet in a side of the refractorymass, (b) a lower tunnel, space below the pair of upper tunnels andarranged in transverse relation thereto and adjacent to an end of therefractory mass, (c) means for interconnecting the pair of upper tunnelsin flow communication with the transverse lower tunnel, and (d) a middletunnel arranged in open flow communication with the transverse lowertunnel and the outlet. The middle tunnel is adapted to form a hot gastrap.

In another preferred embodiment, means positioned adjacent to the uppersurface of the refractory mass, are provided for selectively stirringthe ash residue and at preselected times for removing ash residue fromthe upper surface. The means for stirring and removing comprise at leasttwo degrees of freedom of movement. One exemplary structure includes apair of blades that are each fixedly fastened to an end of a spaced pairof movable shafts. The blades and shafts comprise at least two degreesof freedom of movement, i.e., linear translation and angular rotation,so that the blades may be selectively positioned and oriented relativeto the upper surface of the refractory mass for selectively stirring ashresidue, and at preselected times, for removing the ash residue from theupper surface and into the ash collection cavity.

In a further preferred embodiment, the upper surface of the refractorymass includes an undulant contour such that at least a pair of elongate,concave surface depressions are separated by at least one elongateconvex surface.

In yet another preferred embodiment, the ash residue collection cavitythat is disposed at a bottom of the casing, beside a lower portion ofthe refractory mass, includes a bake-out trough and a cool-down trough.The bake-out trough and cool-down trough each comprise a concave uppersurface defining a channel. These channels are arranged in longitudinalalignment with one another so as to form an elongate concave surface.The cool-down trough is disposed outwardly of the refractory mass at abottom side of the casing so as to be positioned in a lower temperatureportion of the casing. An outlet is defined at a distal end of thechannel for discharging cooled ash residue into a receptacle. Means arepositioned adjacent to an end of the concave surface of the bake-outtrough and spaced from the cool-down trough for selectively stirring theash residue that has collected therein, and at preselected times, forremoving the ash residue from the bake-out trough to the cool-downtrough and for pushing the ash residue into the discharge outlet. Themeans for stirring and removing comprise at least two degrees of freedomof movement. One exemplary structure includes a blade fixedly fastenedto an end of a movable shaft. The blade and shaft comprise at least twodegrees of freedom of movement, i.e., linear translation and angularrotation, so that the blade may be selectively linearly positioned andangularly oriented relative to the channel of the bake-out trough andspaced from the cool-down trough for selectively stirring the ashresidue, At preselected times, the blade and shaft can be oriented andlinearly advanced for removing the ash residue from the bake-out troughto the cool-down trough, and then into the discharge outlet.

The present invention also provides a method of controlling hydrocarbonrelease rate in thermal processing of materials which is designed toovercome the aforementioned problems of conventional incineration. Thehydrocarbon release rate is controlled in a manner which convertssuccessive batches of materials, particularly biomedical wastematerials, of widely varying energy content into substantially harmlessgases and carbon-free residue ash. The residue ash is a sterile, inertinorganic powder, which is non-hazardous, non-leachable and capable ofdisposal as ordinary trash.

Accordingly, the present invention is also directed to a method ofcontrolling the hydrocarbon release rate in the thermal processing andconversion of materials of widely varying energy content in a batchprocessing cycle. The hydrocarbon release rate controlling methodcomprises the steps of: (a) providing a first chamber capable ofreceiving successive batches of feed materials for thermal processingand having widely varying energy content; (b) producing heating in thefirst chamber to cause pyrolyzing of the feed materials into fluidmaterials; (c) providing a second chamber communicating with the firstchamber and capable of receiving the fluid materials from the firstchamber and communicating the fluid materials to a discharge location;(d) producing heating in the second chamber to cause oxidizing of thefluid materials into discharge gases reaching the discharge location;(e) providing a jacketed vessel defining a channel surrounding the firstand second chambers containing a flow of coolant fluid through thechannel; (f) producing separate variable flows of primary and secondaryair respectively into and through the first and second chambers; (g)sensing the temperatures in the first and second chambers; (h) sensingthe temperature of the coolant in the channel of the jacketed vessel;(i) sensing the concentration of a preselected gas in the dischargegases; (j) in response to the temperatures sensed in the first andsecond chambers and jacketed vessel channel coolant and in response tothe concentration of the preselected gas sensed in the discharge gases,controlling primary and secondary flows of air into the first and secondchambers so as to proportion and vary the respective amounts thereof andthereby maintain concentration of the preselected gas in the dischargegases at a preset target corresponding to the generation ofsubstantially harmless discharge gases and production of substantiallycarbon-free residue ash; and (k) in response to the temperatures sensedin the first and second chambers and in the jacketed vessel channelcoolant and in response to the concentration of the preselected gassensed in the discharge gases, selectively stirring an ash residuecollected within said first chamber according to a predetermined patternso as to thereby maintain the concentration of the preselected gas inthe discharge gases at a preset target level corresponding with thegeneration of substantially harmless discharge gases and production ofsubstantially carbon-free residue ash. The preselected gas is preferablyoxygen.

The method also includes the step of mechanically stirring the ashresidue collected in a bake-out trough located in an ash residuecollection cavity within the first chamber. mass.

These and other features and advantages and attainments of the presentinvention will become apparent to those skilled in the art upon areading of the following detailed description when taken in conjunctionwith the drawings wherein there is shown and described illustrativeembodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

In the course of the following detailed description, reference will bemade to the attached drawings wherein like numbers refer to like partsand further wherein:

FIG. 1 is a plan top view of an apparatus for processing of a widevariety of diverse materials, particularly all types of biomedical andother waste materials generated by health care institutions, such ashospitals, formed in accordance with the present invention;

FIG. 2 is a side elevational view of the apparatus of FIG. 1 as seenfrom line 2--2 in FIG. 1;

FIG. 3 is a front end elevational view of the apparatus of FIG. 1, asseen from line 3--3 in FIG. 2;

FIG. 4 is a sectional, elevational view, as taken along lines 4--4 inFIG. 2, of a first housing unit of the apparatus;

FIG. 5 is a first longitudinal, vertical sectional view, as taken alonglines 5--5 in FIG. 4, of a preferred pyrolysis chamber and refractorymass;

FIG. 6 is a second vertical sectional view, as taken along lines 6--6 inFIG. 5, of the preferred pyrolysis chamber and refractory mass shown inFIG. 5 showing a middle tunnel and chamber;

FIG. 7 is a transverse view of the preferred pyrolysis chamber andrefractory mass shown in FIG. 5, as taken along lines 7--7 in FIG. 5, astaken along lines 8--8 in FIG. 5;

FIG. 8 is a horizontal transverse cross-section view of the refractorymass shown in FIG. 5, as taken along lines 8--8 in FIG. 5;

FIG. 9 is a cross-sectional view of the preferred pyrolysis chamber andrefractory mass shown in FIG. 6, as taken along lines 9--9 in FIG. 6,further showing the surface contour of the refractory mass, thetransverse lower tunnel, and the middle tunnel;

FIG. 10 is a cross-sectional view, as taken along lines 10--10 in FIG.6, and similar to FIG. 9, but also including a phantom view of theblades of the stirring and mixing means positioned in channels formed inthe surface of the refractory mass that resemble a "W" shape and alsoshowing conduits communicating between an upper portion of the pyrolysischamber and the pair of upper tunnels in the refractory mass;

FIG. 11 is a broken-away, perspective view of the preferred refractorymass showing a portion of the "W" shaped surface and front bake-out andcool-down troughs;

FIG. 12 is a broken-away, sectional view of the cool-down trough;

FIG. 13 is a top plan view of the pyrolysis chamber, showing a pair ofextendable, rotatable blade assemblies and a top view of a residuecollection portion of the invention;

FIG. 14 is a top elevational view of means for stirring and mixing ashresidue disposed on the top surface of the refractory mass, showing apair of shafts, a side on view of a pair of blades located within thepyrolysis chamber and a scraping device shown in a circled portion ofthe FIG. 16;

FIG. 15 is an end view, partially in phantom, of the blades of thestirring and mixing device illustrating extreme rotationally selectedpositions relative to the surface of the refractory mass;

FIG. 16 is a sectional view of the scraping device circled in FIG. 14;

FIG. 17 is a broken-away view of a ball-screw adapted for telescopicallymoving the shafts of the stirring and mixing device within the pyrolysischamber;

FIG. 18 is an enlarged top elevational view of a portion of the motivemeans shown in FIGS. 17 and 19;

FIG. 19 is an elevational view of a motive power source used forproviding rotational and translational motive force to the stirring andmixing device;

FIG. 20 is a side elevational, cross-sectional view as taken along lines20--20 in FIG. 2;

FIG. 21 is a perspective view of a support carriage and extendable,rotatable blade assembly;

FIG. 22 is a perspective view of the support carriage shown in FIG. 20;

FIG. 23 is a cross-sectional view of the assembly shown in FIG. 20, astaken along lines 23--23 in FIG. 20;

FIG. 24 is a top, cross-sectional view of the residue collection barrelassembly portion of the apparatus;

FIG. 25 is a side view as taken along lines 25--25 in FIG. 24;

FIG. 26 is a side cross-sectional view of the residue collection barrelassembly portion of the apparatus as taken along lines 26--26 in FIG.25;

FIG. 27 is a 90° rotated, side elevational view of a residue collectioncontainer and support frame;

FIG. 28 is a top view of the container shown in FIG. 27;

FIG. 29 is a cross-sectional view of the support frame shown in FIG. 27;

FIG. 30 is a side elevational view of the container and support framesshown in FIG. 27;

FIG. 31 is a top view of the residue collection portion of theapparatus, having the support frame rotated outwardly for removal andinsertion of a container;

FIG. 32 is a block diagram of a coolant fluid circulation circuitemployed by the apparatus;

FIG. 33 is a functional block diagram of the material processingapparatus;

FIG. 34 is a graph of the target oxidation concentrations versus time;and

FIG. 35 is a graph of the target oxidation concentrations versusoxidation chamber temperatures.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following description, it is to be understood that such terms as"forward", "rearward", "left", "right", "upwardly", "downwardly", andthe like, simply refer to the orientation of the structure of theinvention as it is illustrated in the particular views shown in thedrawings when the specific figure faces the reader. Similarly, the terms"inwardly" and "outwardly" generally refer to the orientation of asurface relative to its axis or elongation, or axis of rotation, asappropriate. Also, the terms "connected" and "interconnected", when usedin this disclosure to describe the relationship between two or morestructures, means that such structures are secured or attached to eachother directly or indirectly through intervening structures, andincludes pivotal connections. The term "operatively connected" meansthat the foregoing direct or indirect connection between structuresallows such structures to operate as intended by virtue of suchconnection.

Referring now to the drawings, and particularly to FIGS. 1-4, there isillustrated an exemplary apparatus 1 for controlled thermal processingof waste materials 3, and in particular for controlled disposal ofbiomedical waste materials, which is operated in accordance with ahydrocarbon release rate controlling method. Material processingapparatus 1 basically includes a coolant jacketed vessel 5 defining atleast a first pyrolysis chamber 10. A second, oxidation chamber and mainheat exchanger 400 are also enclosed by coolant jacketed vessel 5, andare more fully disclosed in the foregoing cross-referenced patents. Theapparatus also includes one or more first heater units 25 having aplurality of elongated rod-like electric heating elements mounted in thevessel and being operable to electrically generate heat for pyrolyzingmaterials in first chamber 10, and one or more second heater units 27having a plurality of electric heating elements mounted in the vesseland being operable to electrically generate heat materials in secondchamber 20.

The apparatus further includes an air flow generating means, preferablyan induction fan and a fan speed controller (indicated generally at 30),connected in flow communication with first chamber 10 and second chamber20, and first and second airflow inlet valves 33, 36 connected tojacketed vessel 5. The apparatus also includes an air intakeproportioning valve (not shown) connected in flow communication with thefirst and second air inlet valves. Induction fan 30, the proportioningvalve, and first and second inlet valves 33, 36 function to produceseparate primary and secondary variable flows of air respectively intoand through first chamber 10 and second chamber 20. One suitableembodiment of the fan speed controller is a commercially-available unitidentified as GPD 503 marketed by Magnetek of New Berlin, Wis. Onesuitable embodiment of the valves is disclosed in U.S. Pat. No.4,635,899, the disclosure of which is incorporated herein by reference.One suitable embodiment of the proportioning valve is a pair ofconventional air intake butterfly valves controlled by a standardproportioning motor marketed by the Honeywell Corporation. Therespective amounts of air in the primary and secondary flows drawnthrough the first and second chambers by operation of the induction fanare proportioned by the operation of the proportioning valve toseparately adjust the ratio of the amounts of air flow routed to thefirst and second air inlet valves 33, 36. The respective amounts of airdrawn in the primary and secondary flows are correspondingly varied byvarying the speed of operation of the induction fan.

At least three temperature sensors 37, 38, 39 (FIG. 33) such asconventional thermocouples, are mounted on vessel 5 for sensingtemperatures in first chamber 10 and second chamber 20, and in thecoolant circulating about a channel 40 (FIG. 4) defined by jacketedvessel 5 about first chamber 10 and second chamber 20. Additionally, agas sensor 42 (FIG. 33) is mounted on a discharge outlet of vessel 5 forsensing the concentration of a predetermined gas, for example oxygen, inthe discharge gases. Also, a computer-based central control system 44(FIG. 33) is incorporated in the apparatus for controlling and directingthe overall operation of the apparatus in accordance with a hydrocarbonrelease rate controlling method. One suitable computer which can beemployed by the control system is a PC-55 marketed by the WestinghouseElectric Corporation of Pittsburgh, Pa.

For many applications, material processing apparatus 1 can be providedin the form of a single unit where all components of the apparatus arecontained within the one unit. However, in order to accommodate spaceand installation requirements, there are other applications wherematerial processing apparatus 1 needs to be provided in the form of twoseparate first and second units. Still referring to FIGS. 1-4, materialprocessing apparatus 1 includes a casing 47 having an outer wall 51 andan inner wall 53 disposed in spaced, confronting relation to oneanother, thus forming a coolant jacketed, airtight pressure vessel 5inside of inner wall 53, with channel 40 defined between outer and innerwalls 51, 53. Channel 40 surrounds vessel 5 and contains a flow ofcoolant fluid, such as water. The above-identified related patents showexamples of the circulation flow path of coolant fluid about similarvessel channels. As mentioned above, vessel 5 is separated into firstand second units and has means in the form of a pair of tubularextensions of the outer and inner walls which are fastened together tointerconnect the first and second units in flow communication with oneanother.

Referring to FIGS. 4-10, vessel 5 defines first pyrolysis chamber 10having an inlet 60 and second oxidation chamber 20 connected incommunication with first pyrolysis chamber 10 and having a dischargeoutlet 80. First chamber 10, in which waste materials 3 will bepyrolyzed, receives materials through inlet 60, via operation of anautomatic feeding system 65. Material 3, through pyrolysis, or burningin a starved oxygen atmosphere, is converted to a gas that tends tocongregate in an upper portion 68 of first chamber 10. This gas exitsfirst chamber 10 by passing into an entrance 70 disposed in inner walls53, and flows through a down-draft duct or conduit 72 into and through asystem of tunnels 73 formed in a refractory mass 75 (FIGS. 5 and 6). Itshould be understood that in some of the various cross-sectional viewsof apparatus 1, only one down-draft duct or conduit 72 can be seen,however, a preferred embodiment of the invention will comprise two suchdown-draft ducts 72 disposed in confronting relation to one another inopposing portions of inner wall 53 and outer wall 51, so that adown-draft duct or conduit 72 will be positioned on each side ofrefractory mass 75 (see FIG. 10). Second chamber 20 receives thepyrolyzed materials from first chamber 10 and, after oxidizing thepyrolyzed materials therein, discharges the oxidized materials therefromthrough discharge outlet 80.

Referring to FIGS. 5-10, a series of passages or tunnels 73 are definedin mass of refractory material 75. As the pyrolyzed gas flows downthrough each down-draft duct or conduit 72 from upper portion 68 ofpyrolysis chamber 10, it enters a respective upper tunnel 82, defined inrefractory mass 75. The gas enters refractory mass 75 through an inletopening 74 defined in each side of refractory mass 75, adjacent to anexit opening 76 (FIG. 10) of one of the down-draft ducts or conduits 72.The gas passes through each upper tunnel 82 toward a transverse lowertunnel 85. The gas then flows toward the middle of refractory mass 75until it enters a middle tunnel 87 that forms an inner trap or chamber20. Chamber 20 typically houses gas at a temperature of from about2,000° F. to about 2,200° F., whereas primary chamber 10 contains gasesat a temperature of from 300° F. to 600° F. The hot gas then flowstoward discharge opening 80 where the oxidized gas passes down to alower tunnel, where further turbulence is generated by a series ofvertically oriented rods disposed within opening 80, after which the gasflows to the second unit.

The series or arrangement of tunnels 73 formed in refractory mass 75define the primary section of chamber 20, and provide communication withthe first chamber 10, via down-draft ducts or conduits 72, disposedwithin the side walls of chamber 10. Refractory mass 75 is, of course,surrounded by jacketed vessel 5 and maintained in a heated condition atelevated temperatures by the heating produced in the first chamber bythe first heater units 25 and by the pyrolyzing and oxidizing ofmaterials 3.

Middle tunnel 87 defines chamber 20 where hot gas (2,000-2,200° F.) fromin the lower section of refractory mass 75 is trapped, and preventedfrom flowing back up into pyrolysis chamber 10. Hot gas from chamber 20could explode, under certain conditions, if it were to mix with thehigher oxygen content, lower temperature gasses located in upper portion68 of pyrolysis chamber 10. For example, if there is a rapid shut downof apparatus 1 (e.g., a power outage) where the induction fan is turnedoff, then, after a while, gasses in the pyrolysis chamber cool down dueto the cooling effect of the water flowing in channel 40 of vessel 5. Inthis situation, the lower, hotter gas located in chamber 20 ofrefractory mass 75 would normally tend to flow upwardly, and could mixwith oxygen in chamber 10. It being understood that the lower, hottergas in chamber 10 is oxygen depleted, whereas the upper cooler gas is,relatively, oxygen rich. However, the trap created by chamber 20 ofmiddle tunnel 87 prevents hot gases from moving back up throughdown-draft ducts or conduits 72, due to the difference in densitybetween the gasses in upper portion 68 and chamber 20, among otherfactors. As a result, the lower, hotter gas will tend to remain trappedin chamber 20 of middle tunnel 87, and not move back up throughdown-draft ducts or conduits 72 and into pyrolysis chamber 10.

Refractory mass 75 also includes an upper exterior surface 100 which isexposed to first chamber 10 and below which resides system of tunnels73. Upper surface 100 comprises an undulant contour that, in transversecross-section (FIGS. 9, 10, 11, 17 and 20), resembles a letter "W" inshape. As viewed in FIG. 11, upper surface 100 comprises a pair ofelongate, concave surface depressions (gullies) 105 separated by oneelongate convex surface (rib) 107. Upper surface 100 is preferablycoated with a refractory grade surface coating 109. The undulant contourof upper surface 100 provides for greater surface area to be in contactwith waste material 3, thereby transferring greater heat to thesematerials. Also, upper surface 100 is inclined at about 8°-10° slope sothat it slopes downwardly, toward the wall of vessel 5 through whichmaterial 3 is introduced into chamber 10. The inclined arrangementprevents low caloric content waste materials, e.g., liquid water, fromspilling off of upper surface 100 and into bake-out trough 110.

The undulant surface contour of upper surface 100 also helps to positionnewly introduced materials 3 (typically in the form of a sealed paperboard container or box housing medical waste or the like) above the ashresidue (not shown) that has been formed from pyrolyzing previouslyintroduced waste material and thereby allowing for more even andthorough pyrolyzation of the newly introduced waste material. Inparticular, the undulant contour of upper surface 100 prevents the newlyintroduced material 3 from mixing with lower temperature water that maybe resident in gullies 105. In this arrangement, a box containing wastematerial 3 is placed in first chamber 10 through inlet 60. The box fallsinto first chamber 10 and onto rib 107, where it is prevented fromcompletely engaging the ash residue and water that may be collecting ingullies 105. This arrangement also helps to maintain at least somedirect contact between upper surface 100 of refractory mass 75 and thenewly introduced waste material.

The heated condition of refractory mass 75 causes heating and pyrolyzingof materials 3 which come in close proximity to upper surface 100. Bythe provision of the refractory mass, and maintenance of its heatedcondition at elevated temperatures, the waste material in first chamber10 which comes in close proximity to or contact with the upper surface100 (via contact with at least rib 107) is being continuously heatedfrom underneath by the refractory mass. This construction increasespyrolyzation of difficult to pyrolyze materials present in the firstchamber, and contributes to the substantially complete conversionthereof to a carbon-free ash residue.

The heating effect at upper surface 100 is enhanced by the use ofstirring and mixing means 120 (FIGS. 13-19) which, according to astirring sequence or "recipe" defined by the overall condition of theresidue mass (e.g., the sensed temperature, hydrocarbon content, etc.)allows for the nearly complete conversion of the waste material. Onepossible form of stirring and mixing means 120, that is contemplated foruse in the present invention, is an extendable, rotatable blade assembly125 (ERB assembly 125). Each ERB assembly 125 comprises a shaft 130, astirring blade 135, a shaft scraper 140, and means 145 for moving shaft130 and stirring blade 135. More particularly, each shaft 130 includes aconventional cooling system 133 (FIG. 18) located along its length andadapted to maintain shaft 130 at a lower temperature than that ofchamber 10. In one embodiment, shaft 130 has air circulated through itsinterior to maintain its temperature within specified limits. Shafts 130are arranged so that they pass through inner and outer walls 53, 51, insubstantially parallel relation to one another, and below inlet 60. Inthis way, the portion of shafts 130 located at any given time withinchamber 10, are positioned in spaced, overlying relation to gullies 105of upper surface 100 of refractory mass 75. Shaft scrapers 140 provide athermally sealed and gas tight interface in walls 51, 53, through whichshafts 130 may pass into chamber 10. Shaft scrapers 140 also help toremove any debris, e.g., ash residue, that may collect on the outersurface of shafts 130 while they are resident in chamber 10.

Referring to FIG. 15, stirring blades 135 preferably comprise paddleshaped plates of high temperature metal or ceramic, having a first end147 that is adapted to be fixed to an end of a shaft 130 and a secondend 149 that is somewhat rounded so as to complement the surface contourof gullies 105. As shown in FIG. 15, second end 149 may include aflattened corner portion 151 that complements a flatten bottom surfaceof each gully 105.

Means 145 for moving shafts 130 and stirring blades 135 may comprise anyelectromechanical or hydraulic or pneumatic device of a type known formoving supported shaft type structures, as long as means 145 is capableof imparting two degrees of freedom of movement to shafts 130 andstirring blades 135, i.e., means 145 must be capable of moving theshafts linearly, into and out of chamber 10, while at the same timeimparting selective rotational motive force to the shafts so thatstirring blades 135 are selectively rotated into and out of gullies 105of upper surface 100.

For example, a ball screw 155 (FIG. 17) or hydraulic cylinder (notshown) may be used to actuate ERB assembly 125. Each ERB assembly 125 isoperated separately, and independently of the other according to a setprogram, library of routines or recipes in response to sensor data onhydrocarbon and gas concentration, gas flow, and temperature. If apreselected change in the range of any of these, or other parameters, issensed, then ERB assembly 125 (also called stirrers) is activated tostir the ash residue by a preselected series of linear and rotationalmovements. For thorough combustion or pyrolysis, ash material must bestirred periodically and spread out over upper surface 100. Whenpyrolysis has neared an end, or finished, shafts 130 are fully extendedby means 145, from the end of upper surface 100 closest to inner wall 53of vessel 5, with stirring blades 135 rotated so that flattened cornerportions 151 are placed into full engagement with the bottom surface ofeach gully 105, and the collected ash residue is pushed off, over theend of refractory mass 75 and into bake-out trough 110.

If only a single degree of freedom push arm or lever is used to push ashresidue off upper surface 100, metal objects may be caught between uppersurface 100 and blade 135. This condition would either break the bladeor jam it, or bind it, or cause the obstructing object to dig into thesurface coating. With the present invention, if ERB assembly 125 is in apushing mode and a jam is sensed, then by merely rotating the shaftupwardly, a little, to get over the obstruction, the jam can be cleared.Also, by rotating each blade 135 according to a preset recipe, differentamounts of material may be stirred, as needed. Further, blade 135 mustbe rotated completely out of the way when a new box of waste material 3is dropped through inlet 60 onto upper surface 100. Of course, it willbe understood that a single blade and shaft structure may also be usedwithout departing from the present invention, as an equivalent structureto a pair of blades and shafts, as long as they can move in twodirections, i.e., linearly and rotatable. Likewise, more than two bladesand shafts may also provide means for stirring and mixing the ashresidue. By stirring the ash residue with ERB assembly 125, it ispossible to separate newly introduced waste material from prior, alreadypyrolyzed waste material.

As shown in FIGS. 17-19, one possible means for moving ERB assembly 125comprise a ball nut 160 attached on a bracket 163 to support one end ofshaft 130. Ball nut 160 moves on ball screw 166 and a guide rod 168guides the shaft and blade structure as it moves in and out of chamber10. A hydraulic motor 170 with a belt, or chain and pulley 173 forrotating ball screw 166 may be used to move shaft 130 linearly, in andout, of chamber 10. Another hydraulic motor 175 with a belt or chainpulley 178 may be used to rotate shaft 130, and thus blade 135 withinchamber 10. A conventional shaft encoder, or other known sensor is usedto record the angular position of blade 135 relative to the center ofshaft 130 and upper surface 100. As shown in FIG. 18, cooling system 133comprises a system of ducts running the length of shaft 133 and beingadapted to circulate coolant introduced through coolant port 180,located at a proximal end of shaft 130.

The present invention utilizes three stages of processing. First, theprimary pyrolysis of waste material 3 is carried out by placing thewaste material onto upper surface 100 of refractory mass 75. About 85%of the volume of waste material 3 is removed at this stage. Then, theash residue is swept off of upper surface 100 of refractory mass 75 bystirring and mixing means 120, e.g., by ERB assembly 125, and intobake-out trough 110 where further primary air is added to the ash, viaprimary air valves 33, so that oxidation rather than pyrolysis, takesplace to get rid of the rest of the hydrocarbons that are present in theash residue. About a 10-15% further reduction in volume of material isaccomplished at this stage. This ash material then is moved to acool-down trough 190 where it cools. At this stage, only about 5% of thevolume of original waste material is left. Once cooled, the remainingash residue is pushed into a barrel 200 for disposal. Bake-out trough110 and cool-down trough 190 are best seen in FIGS. 11 and 12, andcomprise an elongate, relatively narrow concave channel positioned atthe bottom of an ash residue collection cavity 195 defined betweenrefractory mass 75 and the wall of vessel 5 (FIGS. 5 and 6). Cool-downtrough 190 further includes a bore 197, defined in the bottom of thechannel, that communicates with a residue barrel 200.

An extendable, rotatable blade assembly 210 (ERB assembly 210) isarranged to move within ash residue collection cavity 195 from a lowerportion of vessel 5 (FIGS. 1-6, 8, 11-13, and 20-23). ERB assembly 210comprises essentially the same components as ERB assembly 125. Moreparticularly, ERB assembly 210 includes a shaft 230, a blade 235, ashaft scraper 240, and means 245 for moving shaft 230 and blade 235within chamber 10. In addition, ERB assembly 210 includes a supportframe 250 that is adapted to structurally support ERB assembly 210 onthe outside of vessel 5 (FIG. 3). Frame 250 includes an upright support255 and a horizontal support 258. ERB assembly 210 operates in the sameway as ERB assembly 125 disposed on upper surface 100 of the refractorymass 75, in that ERB assembly 210 moves linearly and also rotates inaccordance with a preselected library of routines. An attachment may befitted over the end of blade 235 to increase its surface area, andallows it to conform more to the shape of bake-out trough 110 andcool-down trough 190. Further, rather than using ball screw 160, ERBassembly 210 includes a hydraulic cylinder 260 that moves shaft 230linearly, with shaft 230 being supported on a support carriage 262.Carriage 262 has wheels 263 that ride on a track 268 to provide meansfor moving ERB assembly 210 linearly. ERB assembly 210 mixes and stirsash residue in bake-out trough 110 and also moves ash residue intocool-down trough 190. As a consequence, shaft 230 and carriage support262 are longer than ERB assembly 125 and shaft 130.

As shown in FIGS. 11 and 20, the channels forming bake-out trough 110and cool-down trough 190 are in alignment. Cool-down trough 190 hasinsulation around it, and a water wall 270 adjacent to it. Disposedbelow opening 197, in cool-down trough 190, are a pair of slide gates275 that run in racks 277, and are operated by hydraulic cylinders 280.Before opening gates/doors 275, barrel 200 must be brought up intocontact with a seal 285 of opening 197 in order to maintain theintegrity of the closed system. Barrel 200 is supported on a carriage287 having pivotal arms 289 adapted for grasping a lower edge of barrel200 and holding the barrel securely. Carriage 287 is mounted on apivoting arm 288 that allows barrel 200 to pivot under or away from,opening 197. Barrel 200 is lifted off the ground and up against seal285. This operation is completed by a cable and loop 290 that go throughpulleys 293 and a crank 297 to lift barrel in place. Once barrel 200 isin correct sealed position, slide gates 275 open and barrel 200 isfilled with ash. Once barrel 200 is filled, gates 275 are then closed,and barrel 200 lowered and swung out on pivoting arm 288 for removal.

Referring to FIGS. 32-35, there is functionally illustrated thecomponents of and the operative steps performed by material processingapparatus 1 under the monitoring and control of computer-based centralcontrol system 44 for effecting optimal pyrolyzing and oxidizing ofmaterials 3 therein to provide control of the hydrocarbon release ratein accordance with the present invention. FIGS. 32 and 33 providefunctional block diagrams of material processing apparatus 1,illustrating the directions of interactions between the components ofthe apparatus to maintain the target oxygen concentration and therebycontrol the hydrocarbon release rate. FIGS. 34 and 35 are a graphicalrepresentation of the target oxygen concentration versus time and versustemperature, respectively.

Basically, material processing apparatus 1 operates through one cycle tothermally process, that is, to pyrolyze and oxidize, a predeterminedbatch of material 3, such as biomedical waste material, typically ofwidely varying energy values or contents. Central control system 44functions to operate and regulate material processing apparatus 1 duringeach batch processing cycle by controlling the operation of the firstand second heater units 25, 27, the position of the air intakeproportioning valve and the speed of the induction fan 30A and 30B.Central control system 44, under control and direction of a softwareprogram stored in its internal memory repetitively, and at high speed,receives inputs, processes the inputs, and generates outputs. The inputsreceived by central control system 44 from the various temperature andgas sensors contain information about the current states of thepyrolysis process and of the oxidation process. Proportional, Integral,Derivative (PID) control algorithms for regulating induction fan speed30A, proportioning valve position, and recipe/sequences for mixing andstirring means 120 and 210 are contained in the software program. Thesealgorithms are employed by central control system 44 to process theimputed information by integrating the information into a logicalsequence of decision steps and then generating an appropriate set ofoutput instructions to ensure that the pyrolysis and oxidation processesand thus the hydrocarbon release rate continue at an optimum level.

Underlying the present invention is recognition by the inventors hereinthat the direct correlation or correspondence between the hydrocarbonrelease rate and the concentration of a preselected gas, preferablyoxygen, in the discharge gases can be used to control the hydrocarbonrelease rate during operation of the apparatus. For the apparatus to beable to accommodate feed materials of widely varying energy contents asis needed in most waste disposal applications, and certainly withrespect to biomedical waste materials, the apparatus must be operatedwith a hydrocarbon release rate that avoids generation and emission ofunburned hydrocarbons. However, it is not possible to determine inadvance the energy value or content of the batches of material which arefed into the apparatus in order to be able to adjust the operation ofthe apparatus to arrive at the desired hydrocarbon release rate. Theinventors herein recognized that due to the direct correspondencebetween the oxygen concentration in the discharge gases and thehydrocarbon release rate, if only the oxygen concentration is controlledand maintained at a desired target then automatically the hydrocarbonrelease rate is controlled and maintained at the desired optimum level.

More particularly, if the hydrocarbon release rate begins to exceed theoptimum level, this will result in the occurrence of an oxygenconcentration in the discharge gases lower than the desired presettarget. This deficiency will be detected by the oxygen sensor in theheat recovery exhaust and transmitted to the control system. The controlsystem will then adjust the proportioning valve to reduce the air flowinto the pyrolysis or first chamber and increase it to the primarysection of the oxidation or second chamber. As less oxygen is let intothe first chamber, heat generation by pyrolysis reaction in this chamberis reduced. Since the first chamber is surrounded by the coolantjacketed vessel, the surface of the waste materials therein will becooled and thereby lower the hydrocarbon release rate to the optimumlevel. This effect will be further enhanced by appropriate mixing of theash residue atop refractory mass 75 and in bake-out trough 110 accordingto a set of preselected recipes.

It is thought that the present invention and many of its attendantadvantages will be understood from the foregoing description and it willbe apparent that various changes may be made in the form, constructionand arrangement of the parts thereof without departing from the spiritand scope of the invention or sacrificing all of its materialadvantages, the forms hereinbefore described being merely preferred orexemplary embodiments thereof.

What is claimed is:
 1. A waste material processing apparatus,comprising:(a) a casing having a top and bottom and a plurality of sidesdefining a pyrolysis chamber for receiving and pyrolyzing feed materialsinto fluid materials, said pyrolysis chamber having an upper portion fortemporarily receiving said fluid materials; (b) a mass of refractorymaterial contained in said casing, spaced below said upper portion ofsaid pyrolysis chamber and extending between said sides, said refractorymass including (i) an upper surface defining a bottom of said pyrolysischamber, (ii) an end spaced from a first one of said sides of saidcasing for defining an ash residue collection cavity, (iii) a firstside, (iv) a second side, and (v) a bottom; and (c) a system of tunnelsdefined within said refractory mass being spaced below said uppersurface, said system of tunnels including (i) two inlets defined in saidrefractory mass, one inlet defined in said first side and one inletdefined in said second side and both arranged below said upper surface,said inlets communicating directly with said upper portion of saidpyrolysis chamber so as to receive a flow of said fluid material, and(ii) an outlet defined in said bottom for discharging the flow of saidfluid materials from said system of tunnels, said system of tunnelsfurther including:(a) a pair of spaced upper tunnels, one of said pairdisposed in flow communication with said first side inlet and the otherone of said pair disposed in flow communication with said second sideinlet; (b) a lower tunnel spaced below and in transverse relation tosaid pair of upper tunnels and positioned adjacent to an end of saidrefractory mass; (c) means for interconnecting said pair of uppertunnels in flow communication with said transverse lower tunnel; and (d)a middle tunnel arranged in open flow communication with said transverselower tunnel and said outlet.
 2. Apparatus according to claim 1 whereinsaid pair of spaced upper tunnels are substantially parallel to oneanother.
 3. Apparatus according to claim 1 wherein said lower tunnel isarranged substantially parallel to said ash residue collection cavity.4. Apparatus according to claim 1 wherein means for interconnectingcomprises downwardly sloping passageways communicating between saidupper tunnels and said lower tunnel.
 5. Apparatus according to claim 1comprising a middle tunnel positioned between said upper tunnels, inflow communication between said lower tunnel and said outlet anddefining a chamber therebetween for trapping fluid material andpreventing said fluid material from flowing toward said pyrolysischamber.
 6. Apparatus according to claim 5 wherein said fluid materialtrapped within said chamber comprises a gas at a temperature of fromabout 2,000° F. to about 2,200° F.
 7. Apparatus according to claim 6wherein said fluid material within said pyrolysis chamber comprises atleast one gas at a temperature of from 300° F. to 600° F.
 8. A wastematerial processing apparatus, comprising:(a) a casing having a top, abottom, and a plurality of sides defining a pyrolysis chamber forreceiving and pyrolyzing feed materials into fluid materials, saidpyrolysis chamber including an upper portion for temporarily receivingsaid fluid materials and wherein at least one of said plurality of sidesincludes a down-draft duct having (i) an entrance positioned in flowcommunication with said upper portion of said pyrolysis chamber, and(ii) an exit spaced from said entrance; (b) a mass of refractorymaterial contained in said casing, spaced below said upper portion ofsaid pyrolysis chamber and extending between said sides, said refractorymass including (i) an upper surface defining a bottom of said pyrolysischamber, (ii) an end spaced from a first one of said sides of saidcasing for defining an ash residue collection cavity and (iii) a bottom;and (c) a system of tunnels defined within said refractory mass beingspaced below said upper surface, said system of tunnels including atleast one inlet defined in said refractory mass so as to receive a flowof said fluid material and communicating with said exit of saiddown-draft duct, and (ii) an outlet defined in said bottom fordischarging said flow of said fluid materials from said system oftunnels.
 9. Appparatus according to claim 8 wherein said system oftunnels provide flow communication between said pyrolysis chamber and achamber defined within said refractory mass for trapping fluid materialand preventing said fluid material from flowing toward said pyrolysischamber.
 10. Apparatus according to claim 8 comprising two down draftducts positioned in confronting opposed relation to one another withinsaid plurality of sides.
 11. A waste material processing apparatus,comprising:(a) a casing having a top, a bottom, and a plurality of sidesdefining a pyrolysis chamber for receiving and pyrolyzing feed materialsinto fluid materials, said pyrolysis chamber including an upper portionfor temporarily receiving said fluid materials and wherein two of saidplurality of sides each includes a down-draft duct having (i) anentrance positioned in flow communication with said upper portion ofsaid pyrolysis chamber, and (ii) an exit spaced from said entrance; (b)a mass of refractory material contained in said casing, spaced belowsaid upper portion of said pyrolysis chamber and extending between saidsides, said refractory mass including (i) an upper surface defining abottom of said pyrolysis chamber, (ii) an end spaced from a first one ofsaid sides of said casing for defining an ash residue collection cavity,and (iii) a bottom; and (c) a system of tunnels defined within saidrefractory mass being spaced below said upper surface, said system oftunnels including two inlets defined in said refractory mass so as toreceive a flow of said fluid material and each communicating with anexit of one of said down-draft ducts, and (ii) an outlet defined in saidbottom for discharging said flow of fluid materials from said system oftunnels, said system of tunnels further including:(a) a pair of spacedupper tunnels, each one of said pair of upper tunnels being disposed inflow communication with one of said inlets; (b) a lower tunnel spacedbelow and in transverse relation to said pair of upper tunnels andpositioned adjacent to an end of said refractory mass; (c) means forinterconnecting said pair of upper tunnels in flow communication withsaid transverse lower tunnel; and (d) a middle tunnel arranged in openflow communication with said transverse lower tunnel and said outlet.12. Apparatus according to claim 11 wherein said pair of spaced uppertunnels are substantially parallel to one another.
 13. Apparatusaccording to claim 11 wherein said lower tunnel is arrangedsubstantially parallel to said ash residue collection cavity. 14.Apparatus according to claim 11 wherein means for interconnectingcomprises downwardly sloping passageways communicating between saidupper tunnels and said lower tunnel.
 15. Apparatus according to claim 11comprising a middle tunnel positioned between said upper tunnels, inflow communication between said lower tunnel and said outlet anddefining a chamber therebetween for trapping fluid material andpreventing said fluid material from flowing toward said pyrolysischamber.
 16. Apparatus according to claim 15 wherein said fluid materialtrapped within said chamber comprises a gas at a temperature of fromabout 2,000° F. to about 2,200° F.
 17. Apparatus according to claim 16wherein said fluid material within said pyrolysis chamber comprises atleast one gas at a temperature of from 300° F. to 600° F.
 18. Appparatusaccording to claim 11 wherein said system of tunnels provide flowcommunication between said pyrolysis chamber and a chamber definedwithin said refractory mass for trapping fluid material and preventingsaid fluid material from flowing toward said pyrolysis chamber. 19.Apparatus according to claim 11 comprising two down draft ductspositioned in confronting opposed relation to one another within saidplurality of sides.